Ask a Scientist: Warts aren’t just for witches and goblins

Dr. Diana McShane is an assistant professor of dermatology at UNC-Chapel Hill. Here, she explains how warts – which pop up this time of year on the faces of Halloween witches and goblins – can develop in real life. Questions and answers have been edited.

Q. What causes warts?

A. Warts are caused by infection with the human papilloma virus (HPV), of which there are over 100 different types. Some types cause typical warts on the hands and body, others cause the bigger plantar warts, some cause smaller flat warts and still other types cause genital warts. Most of the HPV virus types cause benign growths in the skin. But a few types, particularly those that cause genital warts, can be associated with cancer later in life.

Q. Are warts contagious?

A. Common warts are more often spread from contact with objects that are carrying the virus. Essentially, a person with a wart touches something and transmits the HPV virus to that object. Then, another person touches that object and obtains the virus, particularly if there is an area of injury at the site of contact. However, the genital warts that appear in private areas are spread from direct person-to-person contact.

Q. Why do kids seem to get warts more often than adults?

A. Children have common warts more frequently because they have not yet developed the immunity against those virus types. People have to be exposed to the virus, to then get the warts, to then allow the immune system to develop the ability to get rid of those warts. Once the immune system has learned to fight that type of virus, it can use that information to prevent the virus from causing warts in the future.

As adults, we’ve had time to be exposed to several wart types and our immune system has learned to fight them. We also tend to have fewer injuries as adults and therefore fewer opportunities for the virus to get past our first defense: our intact skin.

Q. What treatments are most effective in getting rid of warts?

A. There are many options for treatments of warts, which means none of them are perfect. Most are aimed at destroying the tissue that contains the wart (killing it), increasing the immune response against the wart, stopping the virus from making more of itself, or any combination of the above.

Large reviews of the scientific literature suggest that salicylic acid and cryotherapy (freezing with liquid nitrogen) are effective, but smaller studies have also shown improvement with many alternative therapies such as imiquimod, cantharidin, podophyllin, 5-fluorouracil, yeast extract, squaric acid, and laser. Many of the options are uncomfortable and require multiple treatments to be effective.

For genital HPV and the potential associated cancers, prevention is key. I recommend getting the HPV vaccine and using protection during sexual activities.

This story was originally published October 25, 2015 at 12:18 AM with the headline "Ask a Scientist: Warts aren’t just for witches and goblins."